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PREOPERATIVE CARE: LESION- LESION-SPECIFIC MANAGEMENT

In document Pediatric_Cardiology.pdf (Page 56-66)

CHAPTER Critical Heart Disease in the Newborn

PREOPERATIVE CARE: LESION- LESION-SPECIFIC MANAGEMENT

A very practical approach to critical CHD is to consider lesions in terms of the timing of presentation and catego-rizing them as follows: (1) “shock” in the delivery room, (2) “symptoms” on the first day of life, and (3) “symp-toms” in the first week of life. Understanding the physiol-ogy that dictates the timing of presentation of severe CHD is the key to prompt diagnosis and appropriate management. In each section, specific lesions will be dis-cussed in detail in terms of pathophysiology, clinical pres-entation, diagnostic assessment, and treatment.

Shock in the Delivery Room

With the disruption of the uteroplacental circulation, the newborn circulation resembles a series configuration, with the right side of the heart functioning to deliver blood to the pulmonary bed for oxygenation and the left side responsible for distributing oxygenated blood for peripheral consumption. If oxygenated blood cannot be adequately presented to the systemic circulation, cardio-genic shock rapidly ensues, resulting in infant demise. As a general principle, cardiac lesions that are unstable in the delivery room represent abnormalities of oxygen delivery that are often not stabilized by PGE1 alone and require immediate intervention in order to sus-tain life.

Hypoplastic Left Heart Syndrome with Intact Atrial Septum

When left ventricular hypoplasia ( HLHS) (Fig. 2-6) and an intact atrial septum ( IAS) are present, effective egress from the left atrium is not possible. Unless a decompress-ing vein is present, there is no means by which the pul-monary venous return can leave the left atrium.

Pulmonary venous obstruction develops and pulmonary hypertension ensues. HLHS with an open atrial septum is discussed later in this chapter.

At the time of delivery, infants with HLHS/IAS present with profound cyanosis, metabolic acidosis, respiratory distress, and cardiovascular collapse. Patients are criti-cally ill, markedly tachypneic, and often have a PaO2 of less than 20 mmHg. Their cardiovascular exam is signifi-cant for a single, loud second heart sound and the absence of a murmur. The chest x-ray (CXR) demon-strates pulmonary venous congestion and a normal car-diac silhouette. Echo confirms the diagnosis with careful examination of left-sided heart structures and interroga-tion of the atrial septum.

As is true for all infants with HLHS, prostaglandin should be administered immediately to ensure ductal patency and systemic perfusion. Immediate

resuscita-tion includes endotracheal intubaresuscita-tion, vascular access, correction of metabolic acidosis, and oxygen, as needed.

Once the diagnosis of HLHS/IAS is made, prompt left atrial decompression is necessary. Emergent transcatheter (balloon and blade atrial septostomy) or surgical (atrial septectomy or stage 1 reconstruction) intervention must be performed to decompress the left atrium and allow for oxygenated blood to reach the circulation.

Despite early and aggressive intervention, survival of infants with HLHS/IAS is poor and may be related to increased pulmonary venous tone developing in utero.11

Transposition of the Great Arteries with Restrictive or Intact Atrial Septum

In a newborn with D-transposition of the great arteries (D-TGA), the aorta is connected to the RV, and the pul-monary artery is connected to the LV. The systemic and pulmonary circulations function in parallel rather than in series, resulting in recirculated Qp and a deficiency of oxygen supply to the tissues.When the atrial septum is intact or very restrictive, mixing between the two circu-lations only can occur at the level of the ductus arterio-sus and results in significantly impaired oxygen delivery to the tissues.

D-TGA/IAS presents at delivery with profound cyanosis and associated metabolic acidosis. The pre- and postductal saturations may demonstrate reverse differ-ential cyanosis (see Fig. 2-2). Despite the intracardiac pathology, the cardiac exam is essentially unremarkable.

Arterial blood gas analysis suggests a combined picture Figure 2-6 Physiology of hypoplastic left heart syndrome. In the situation of aortic atresia, cerebral and coronary arterial blood flow arises retrograde from the patent ductus arteriosus. Increased restriction at the atrial septum decreases Qp:Qs. A patient with an intact or near-intact atrial septum presents with shock in the delivery room because of obstructive pulmonary venous return and inadequate systemic output.

of metabolic and respiratory acidosis, with a PaO2 gener-ally less than 25 mmHg. The CXR shows a narrow medi-astinal shadow, the ECG is usually normal, and the echo confirms diagnosis.

Treatment of the severely hypoxic patient with

D-TGA involves optimizing the mixed venous oxygen content and ensuring adequate mixing of the two paral-lel circulations. PGE1 should be initiated immedia-tely to maintain ductal patency. Maximizing oxygen delivery to the tissues can be accomplished through var-ious maneuvers such as (1) decreasing oxygen con-sumption through sedation and paralysis, (2) optimizing oxygenation with mechanical ventilation and supple-mental oxygen, (3) increasing oxygen delivery by in-creasing cardiac output with inotropic agents (dopamine at 3–5 μg/kg/min), and (4) optimizing blood oxygen-carrying capacity by keeping the hemoglo-bin above 13 g/dL. An emergent balloon atrial sep-tostomy (echocar- diography- or fluoroscopy-guided) must be performed to allow for adequate mixing at the atrial level (Fig. 2-7). Once the baby has recov-ered, definitive surgical correction is performed by

“switching” the great arteries: the aorta is reconnected to the LV and the pulmonary artery to the right, with reimplantation of the coronary arteries into the neoaorta.

Following transcatheter or surgical stabilization of newborns presenting in the delivery room with HLHS/IAS or D-TGA/IAS, end-organ function must be assessed to determine the optimal timing of palliative or definitive surgical intervention.

Symptoms on the First Day of Life

To review, normal physiology at birth is characterized by a dramatic decrease in PVR leading to a conco-mitant increase in pulmonary blood flow, with the lungs assuming the responsibility of oxygenation and venti-lation. Critical CHD that presents prior to ductal clo-sure includes derangements in physiology at two levels: (1) cardiovascular structures resulting in mechani-cal airway compromise (e.g., severe Ebstein’s and TOF with absent pulmonary valve), and (2) inability to deliver oxygenated blood to target systemic tissues (e.g., total anomalous pulmonary venous return with obstruction and D-TGA with restrictive atrial sep-tum).

Airway Compromise

Severe Ebstein’s Anomaly of the Tricuspid Valve Ebstein’s anomaly is characterized by abnormality of the tricuspid valve wherein the septal and posterior leaflets are deformed and displaced inferiorly into the RV. These leaflets are usually rudimentary and

thick-Figure 2-7 Echocardiographic images of a balloon atrial septostomy for transposition of the great arteries.A, A deflated balloon catheter is advanced across the atrial septum to the left atrium, where it is inflated with 2–3 mL of saline.B, The inflated balloon is pulled abruptly across the atrial septum to the right atrium and immediately deflated. After removal of the balloon, the atrial septal defect created can be seen easily on color flow Doppler.

ened and often have abnormal tethered attachments to the ventricular septum. The portion between the true valve annulus and the downwardly displaced leaflets is referred to as the atrialized portion of the RV. In the most severe form of this disease, the tricuspid valve is severely incompetent, resulting in profound right atrial enlargement (Fig. 2-8).

In this most severe form, newborns often present with airway compression from the profound cardiomegaly, functional pulmonary atresia, and resultant right-to-left atrial-level shunt resulting in cyanosis and ductal-depend-ent pulmonary blood flow. Neonatal Ebstein’s can be asso-ciated with anatomic pulmonary atresia. Even in those newborns with a functional pulmonary valve, the combi-nation of a small RV cavity, severe tricuspid regurgitation, and elevated PVR often result in functional pulmonary atresia. Deoxygenated blood is diverted from the right atrium across the foramen ovale and into the systemic cir-culation.

A neonate with severe Ebstein’s anomaly typically presents in the immediate newborn period with respira-tory failure and marked cyanosis. The lungs fields are usually clear to auscultation. The cardiac exam is signifi-cant for a systolic regurgitant murmur, heard best at the left lower sternal border consistent with tricuspid regur-gitation. CXR demonstrates impressive cardiomegaly.

ECG demonstrates right atrial enlargement as evidenced by characteristic peaked P waves in lead II.Widening of the QRS complex consistent with a right bundle branch pattern may be evident.Wolff-Parkinson-White ( WPW ) syndrome is seen in 20–30% of patients with Ebstein’s disease. Even in the absence of WPW, patients with

Ebstein’s are predisposed to a variety of atrial arrhyth-mias. Echo confirms the diagnosis.

Infants should be intubated immediately to relieve the compromised ventilation caused by airway compression.

PGE1must be administered to maintain ductal patency to ensure adequate pulmonary blood flow.Vascular access should be secured; volume expansion, inotropic support, and bicarbonate should be administered judiciously.

Anemia should be corrected in an attempt to maximize oxygen-carrying capacity. In the event that tachyarrhyth-mias are present, adenosine can be used acutely to con-vert reentrant supraventricular tachycardia to normal sinus rhythm. Functional pulmonary atresia may be over-come by lowering PVR. If cyanosis worsens as the duc-tus arteriosus becomes restrictive after discontinuing PGE1, it may be necessary to decrease PVR by using oxy-gen or nitric oxide.12Surgical options for severe neonatal Ebstein’s anomaly include modified Blalock-Taussig shunt placement with atrial reduction procedure or heart transplantation. Despite aggressive medical man-agement, the mortality rate remains quite high for the severe form of this disease.13

TOF with Absent Pulmonary Valve

Congenital absence of the pulmonary valve (i.e., rudi-mentary ridges of pulmonic valve tissue) is a rare defect.

It often is associated with an anterior malalignment VSD and mixed pulmonary valve disease (obstruction and regurgitation) resulting in massive dilation of the proxi-mal pulmonary arteries. This entity has been termed TOF with absent pulmonary valve. The pulmonary trunk and its main branches are often of aneurysmal proportion, resulting in the most severe form with airway obstruc-tion and associated tracheobronchomalacia. In addiobstruc-tion, often there are distal pulmonary artery stenoses.

Severely affected infants present immediately after birth with evidence of respiratory failure. The physical exam reveals tachypnea, subcostal retractions, and cyanosis. The CXR may appear hyperinflated with evi-dence of decreased pulmonary blood f low. The car-diac exam demonstrates a characteristic “to-and-fro”

murmur at the left upper sternal border, consistent with pulmonary outf low obstruction and regurgita-tion. The second heart sound is single and heard most loudly at the base of the heart. Right ventricular hyper-trophy is present on the ECG, but may be difficult to distinguish from normal right-sided voltages in the immediate newborn period. Echo confirms the diagno-sis.

These infants require immediate intubation to ensure adequate ventilation and oxygenation. The prognosis for infants with this disease depends in part on the extent of tracheobronchial abnormalities secondary to the mas-sively dilated branch pulmonary arteries. Infants who present immediately with respiratory distress have a worse prognosis than their counterparts without Figure 2-8 Echocardiographic pictures from a subxyphoid

projection of Ebstein’s anomaly of the tricuspid valve. The leaflets of the tricuspid valve are displaced inferiorly, resulting in a functionally hypoplastic right ventricle ( RV ). LV, Left ventricle.

respiratory symptoms at birth. Some babies have com-pression of their airways that can be surgically relieved with plication of the pulmonary arteries. Others have more diffuse abnormalities of the airway architecture and, despite surgical intervention, continue to require long-term ventilatory management strategies.14

Obstruction to Pulmonary Venous Return

Completion of gas exchange occurs at the alveolar level;

fully oxygenated blood returns to the left atrium through four pulmonary veins, two veins from each side draining the upper and lower segments of each lung field. From the left atrium, blood flows into the left ven-tricle and is ejected into the systemic circulation. If a structural heart lesion obstructs oxygenated blood from entering the systemic circulation, within several hours of life, progressive hypoxemia and resultant metabolic acidosis ensue.

In total anomalous pulmonary venous return ( TAPVR) with obstruction, there is no connection between the pulmonary veins and the left atrium. The pulmonary veins form a confluence behind the left atrium, which decompresses through a vertical vein, usually inferiorly below the diaphragm, and empties either into the por-tal system or into the ductus venosus before ultimately returning to the right atrium. There exists complete mixing of systemic and pulmonary venous return within the right atrium.When the vertical vein enters the portal system, obstruction to pulmonary venous return is pri-marily caused by increased resistance to flow as blood is forced through the hepatic sinusoids before entering the inferior vena cava (Fig. 2-9). In the case where pulmonary venous return drains into the ductus venosus, constric-tion of the ductus venous after birth dramatically increases the resistance. In either scenario, elevated pres-sure in the pulmonary venous channel is transmitted to the pulmonary capillary bed.

Neonates with TAPVR with obstruction usually pres-ent within the first hours to days of life, and the greater the degree of obstruction, the earlier the appearance of clinical manifestations. Infants typically demonstrate cyanosis and evidence of respiratory distress secondary to pulmonary venous congestion. On physical examina-tion, the infant is ill-appearing with evidence of cyanosis and marked tachypnea. TAPVR is a complete mixing lesion; therefore, saturations in the aorta and pulmonary arteries are equal and there is no discrepancy between pre- and postductal saturations. Cardiovascular findings are minimal and the only abnormality appreciated on exam is accentuation of the pulmonary component of the second heart sound. Other features of pulmonary venous congestion are present, including bilateral rales at the lungs’ bases. CXR reveals very characteristic features of a normal cardiac silhouette and progressive pulmonary venous congestion. The ECG is typically unremarkable

when the intracardiac anatomy is normal. Echo confirms diagnosis. The location of each pulmonary vein should be carefully documented, the pulmonary venous confluence pathway of the decompressing vein delineated, and sizing of the left sided heart structures determined. Although left-sided structures may appear small, they most com-monly tolerate the full cardiac output postoperatively.

Treatment for TAPVR is surgical repair, which should be performed as soon as possible. If the infant is critically ill and immediate surgery is not an option, the infant can be stabilized with venoatrial extracorporeal membrane oxygenation while awaiting surgery. Endotracheal intuba-tion should be performed to maximize oxygenaintuba-tion and ventilation. Sedation and neuromuscular blockade will minimize oxygen consumption and peak inspiratory air-way pressures. Vascular access should be secured, vol-ume status maintained, and electrolyte corrections and inotropic support administered if necessary. Although these patients are cyanotic, prostaglandin administration has been reported to worsen the hemodynamic state by further increasing pulmonary blood flow.

Symptoms in the First Week of Life

Postnatal closure of the ductus arteriosus occurs in two stages.Within 12 hours after birth, contraction and thick-ening of the walls of the ductus arteriosus result in its functional closure. The second stage of closure usually takes place over the next week or so as ductal tissue invo-lutes and is ultimately replaced by fibrous connective

Left pulmonary veins

Vertical vein Right

atrium

Figure 2-9 Physiology of infradiaphragmatic total anomalous pulmonary venous return. The pulmonary veins return to a complex behind the left atrium, decompressed by a vertical vein through the diaphragm and ductus venosus to the right atrium.

There is complete mixing of pulmonary and systemic venous return in the right atrium. Obstruction to pulmonary venous return occurs as the vertical vein passes past the diaphragm through hepatic sinusoids or at the ductus venosus.

tissue, sealing the lumen permanently and producing the ligamentum arteriosum.“Ductal-dependent” blood flow describes abnormalities of cardiac physiology with oblig-atory flow across the ductus to maintain systemic or pul-monary perfusion. Patients with ductal-dependent blood flow typically present within the first few days to weeks of life with evidence of cyanosis or systemic hypoperfu-sion. These lesions can be broadly considered in two categories: (1) left-sided obstructive lesions with ductal-dependent Qs, and (2) right-sided obstructive lesions with ductal-dependent Qp.

In addition, patients with significant left-to-right shunting may present with symptoms of congestive heart failure as the PVR falls during the first week of life.

An example of this physiology is truncus arteriosus.

Lesions with Ductal-Dependent Systemic Blood Flow

Although there are multiple levels at which obstruction can occur along the left ventricular outflow tract, neonates with left-sided obstructive disease present with similar clin-ical manifestations suggestive of cardiogenic shock. Signs and symptoms include pallor, “dusky” appearance, cool extremities,“thready” pulses, diaphoresis, tachycardia, and tachypnea. These findings reflect an underlying state with inadequate systemic perfusion, progressive metabolic aci-dosis,and cardiovascular collapse.Infants presenting in this manner are often considered to be septic, and a complete septic work-up is often initiated. The practitioner must consider the possibility of ductal-dependent heart disease, especially when infants present during the first month of life. In addition to antibiotic therapies, one should consider the administration of prostaglandins promptly until a com-plete cardiac evaluation can be obtained.

Hypoplastic Left Heart Syndrome

HLHS is a spectrum of left-heart obstructive lesions resulting in the underdevelopment of the mitral valve, LV, left ventricular outflow tract, aortic valve, and aorta.

Physiologically, the right ventricle is responsible for main-taining both pulmonary and systemic circulation.

Adequate systemic perfusion is dependent on the patency of the ductus arteriosus (see Fig. 2-4).Without treatment, HLHS is uniformly fatal.

The majority of neonates with HLHS present within the first week, manifesting signs and symptoms of shock:

tachycardia, tachypnea, hypotension, cool extremities, poor perfusion, and diminished peripheral pulses. The cardiac exam demonstrates a dominant right ventricular impulse, a normal first heart sound, and a single second heart sound. Occasionally, neonates will have a ductal flow murmur best appreciated at the left upper sternal border. A gallop rhythm can be present, as can evidence of an enlarged liver, both signs of heart failure. Distal extremities are cool and pulses often are difficult to pal-pate. Metabolic acidosis and hypoglycemia usually are

present and indicate inadequate systemic perfusion.

Arterial blood gas analysis reveals metabolic acidosis and a failed hyperoxia test. The ECG can be normal. The CXR typically demonstrates cardiomegaly with increased pul-monary vascular markings. Echo not only establishes the diagnosis but provides important clinical information regarding right ventricular function, tricuspid regurgi-tation, and restriction to atrial-level shunting. HLHS is a combination of mitral stenosis or atresia and aortic stenosis or atresia (Fig. 2-10).

Therapy for preoperative infants with HLHS is outlined above (see Evaluation of Additional Organ Systems:

Cardiovascular).Specifically,ductal patency must be main-tained ( by urgent administration of PGE1) and pulmonary overcirculation and systemic hypoperfusion must be avoided. Management strategies should be focused on manipulating PVR and SVR in a manner that maintains the precarious balance between pulmonary and systemic cir-culations. The goal should be to maintain an arterial pH of

Cardiovascular).Specifically,ductal patency must be main-tained ( by urgent administration of PGE1) and pulmonary overcirculation and systemic hypoperfusion must be avoided. Management strategies should be focused on manipulating PVR and SVR in a manner that maintains the precarious balance between pulmonary and systemic cir-culations. The goal should be to maintain an arterial pH of

In document Pediatric_Cardiology.pdf (Page 56-66)